Chip resistant primer composition VI&#34;

ABSTRACT

A solvent based thermosetting coating composition comprising hydroxy functional epoxy ester resin, linear polycaprolactone diol, and blocked polyisocyanate crosslinking agent. The coating composition may be formulated as hot sprayable, high solids coating composition suitable for use as a chip resistant automotive vehicle primer adapted for use on body panel areas subject to chipping by stones, gravel and other road debris. Alternatively, the composition may be formulated as a high solids composition sprayable with conventional spraying equipment. The hydroxy functional epoxy ester resin is formed by reaction of diepoxide, chain extended with diphenol and dicarboxylic acid, with hydroxy functional secondary amine in chain terminating reaction.

Reference is made to concurrently filed and commonly assigned relatedU.S. application Ser. Nos. 800,886 entitled "Chip Resistant PrimerComposition VI" and 800,943 entitled "Chip Resistant Primer CompositionVI' ", both to Kordomenos et al.

TECHNICAL FIELD

This invention relates to a solvent-based, thermosetting coatingcomposition comprising hydroxy functional epoxy ester resin, highmolecular weight linear polycaprolactone diol and blocked polyisocyanatecrosslinking agent. It relates also to such coating compositionformulated, for example, as a hot sprayable, high solids coatingcomposition suitable for use as a chip resistant automotive vehicleprimer adapted for use on body panel areas subject to chipping bystones, gravel and other road debris.

BACKGROUND

Automobile manufacturers, in their efforts to extend the expected lifeof automobile sheet metal and the like, have directed considerableattention to various processes and compositions designed to result innot only improved corrosion resistance but also improved chip resistanceproperties. In particular, research and development efforts haverecently been directed to obtaining primer compositions which areflexible and chip resistant and which give corrosion protection whileexhibiting good humidity and solvent resistance, as well as goodintercoat adhesion. New automobile designs and concern about chipping inareas exposed to stones, gravel and other road debris, e.g. rockerpanels, have demanded such chip resistant primers which can be appliedin reasonable thicknesses by techniques which do not require extensiveand expensive processing modifications during painting operations. Todate available primers, whether high or low solids, have not provensuitable.

In order to overcome the aforementioned chipping problem it has beencommon to apply relatively thick chip resistant coatings in body panelregions, which are inclined to chip, prior to application of stillanother primer composition. One such chip resistant sealer materialwhich has been employed is a polyvinyl chloride plastisol sealer whichhas been applied with airless spraygun equipment in thicknesses of about20 mils in regions subject to high levels of chipping. Problemsattendant with such thick coatings are readily apparent. Because of thethickness in the region to which it is applied, these materials presentan appearance problem often resulting in waviness and roughness in thefinal coating on the sheet metal. Often times surface imperfections alsoresult from the fact that a primer is applied over the top of thissealer, with the primer and sealer being cured together. As a resultsome solvent and plasticizer tend to be driven out of the polyvinylchloride plastisol and result in a wavy and rough surface. Still furtherproblems associated with the use of such polyvinyl chloride plastisolsealers and the like involve application technique. Since the polyvinylchloride plastisol sealers and the like must be applied in thicknessesof 20 mils or greater in order to obtain good adhesion, they cannot befeathered down to blend in with other regions of the sheet metal whichdo not require the additional chip protection. Thus, the materials mustbe applied using a masking technique whereby those regions which are notto be coated with the sealer material are masked in a separate operationprior to application of sealer. This masking is then removed after thesealer is applied. It would obviously be desirable to eliminate theseadditional steps in the application of the chip resistant sealermaterial.

Accordingly, it is a preferred object of this invention to provide anovel solvent based, thermosetting coating composition adapted for useas a chip resistant primer, which primer may be applied in thicknessesof less than 20 mils and which may be feathered in such a manner as toblend with paint in other areas of the substrate to be painted which donot require chip resistant coating.

It is another object of the invention to provide novel coatingcompositions which comprise hydroxy functional epoxy ester resin, highmolecular weight linear polycaprolactone diol and blocked polyisocyanatecrosslinking agent which provide high crosslinking efficiency and tough,well cured films at minimum bake temperatures such as when applied asautomotive primers. In this regard, it is a particular object of theinvention to provide a novel thermosetting coating composition ofsufficiently low Volatile Organic Content (VOC) to aid in meetinggovernmental emissions guidelines and yet which can be applied to asubstrate by spraying or other known method.

It is another object of the invention to provide a composition whichwill form a coating on a substrate, which coating has advantageousphysical properties including, for example, humidity and solventresistance, flexibility and corrosion protection for the underlyingsubstrate.

Additional aspects and advantages of the invention will be apparent fromthe following description thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, novel thermosetting coatingcompositions are provided which are especially advantageous for use ashigh solids organic solvent based thermosetting coating compositions toprovide chip resistant coatings. The coating composition of thisinvention, in addition to solvent and any pigments and additives suchas, for example, catalysts, flow control agents and the like, comprises:

(A) hydroxy functional epoxy ester resin having a number averagemolecular weight (Mn) between about 1,000 and about 4,000 and being thereaction product of hydroxy functional secondary amine, in chainterminating reaction, in approximately 1 to 1 equivalent ratio with thechain extension reaction product of diepoxide reacted substantiallysimultaneously with diphenol and dicarboxylic acid in amounts sufficientto give a weight per epoxide (WPE) of between about 500 and about 2,500,preferably between about 500 and about 1,500, and the acid and diphenolreacted with the diepoxide being preferably employed in a ratio of 10/90to 90/10;

(B) linear polycaprolactone diol having a molecular weight of betweenabout 1500 and about 5000, preferably between about 2000 and about 4000,wherein (A) and (B) are included in the composition in a weight ratiobetween about 4:1 and about 1:4; and

(C) blocked polyisocyanate crosslinking agent comprising at least twoisocyanate groups which have been blocked by reaction with an activehydrogen bearing blocking agent which de-blocks at the curingtemperature of the composition, the crosslinking agent being included inthe composition in an amount equal to between about 10 and about 50percent of the combined weight of (A) and (B) in the composition.

Particularly preferred compositions of the invention are thoseformulated as high solids coating compositions having solids levels inthe range of 65-80% solids and which are applied as chip resistantprimers in those areas of automotive panels, such as rocker panels,which are exposed to high levels of chipping. Such compositions may beapplied in thicknesses ranging from 1 to 25 mils wet to obtain finalcoatings in the range of 1 to 12 mils dry, and may be feathered down toblend in with paint applied to regions outside that requiring additionalchip resistance protection. Generally, the compositions of this solidslevel may be applied using hot spray equipment at temperatures in therange of about room temperature, i.e., about 70° F., to about 160° F.

Other preferred compositions of the invention are those formulated ashigh solids coating compositions adapted to be applied by conventionalspraying onto a substrate. These high solids coating compositions mayhave a solids level in the range of 50-60% and are especially useful asa primer coating on the bare, unpolished metal surface of an automotivevehicle. As used herein, a high solids coating composition is one havingwhich a volatile organic content of about 479 g/l (4.0 lb./gal.) orless.

Other features and advantages of this invention will become moreapparent from the following, detailed description thereof including thepreferred embodiments and best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

Thermosetting coating compostions of the invention comprise hydroxyfunctional epoxy ester resin, high molecular weight linearpolycaprolactone diol and blocked polyisocyanate crosslinking agent. Thehydroxy functional epoxy ester resin has a number average molecularweight (M_(n)) between about 1,000 and about 4,000 and is the reactionproduct of chain extended diepoxide with hydroxy functional secondaryamine in chain terminating reaction in approximately 1 to 1 equivalentratio. The chain extended diepoxide used in preparing the precursor isthe reaction product of diepoxide reacted substantially simultaneouslywith diphenol and dicarboxylic acid in amounts sufficient to give aweight per epoxide (WPE) of between about 500 and about 2,500,preferably between about 500 and about 1,500. Preferably the acid anddiphenol reacted with the diepoxide are employed in a ratio of 10/90 to90/10. The linear polycaprolactone diol has a molecular weight ofbetween about 1500 and about 5000, preferably between about 2000 and4000. These polycaprolactone diols may be prepared by polymerizinglactone monomers, preferably epsilon-caprolactone monomers, withinitiators comprising one or more compounds having two functional groupseach having an active hydrogen. The hydroxy functional epoxy esterresins and the polycaprolactone diol are included in the coatingcomposition in a weight ratio of between about 1:4 and about 4:1,preferably in a weight ratio of about 1:1.

The blocked polyisocyanate crosslinking agent comprises at least twoisocyanate groups which have been blocked by reaction with an activehydrogen bearing blocking agent, which de-blocks at the cure temperatureof the composition. The blocked polyisocyanate crosslinking agent isincluded in the composition in an amount equal to between about 10 andabout 50 percent, preferably between about 20 and about 40 percent, ofthe combined weight of the hydroxy functional epoxy ester resin andlinear polycaprolactone diol in the coating composition. The blockedpolyisocyanate crosslinking agent preferably is selected from the groupconsisting of, but not necessarily limited to, blocked trifunctionalisocyanurate ring containing polyisocyanates and oligoester modifiedblocked isocyanates.

It is believed to be a significant characterizing aspect of the coatingcomposition of the invention that the linear polycaprolactone diolportion of the composition gives the polymer flexibility as well astoughness, two key properties when choosing a primer for use in areassusceptible to chipping. It is a further characterizing aspect of thecomposition that it includes epoxy resin portions, i.e. from thehydroxyl functional epoxy ester resin of the composition, which give thecopolymer excellent corrosion resistance properties. Still further, itis a characterizing aspect of the invention that the compositioncontains tertiary amine groups (i.e., since hydroxy functional secondaryamines are used to form the hydroxy functional epoxy ester resin,tertiary amine groups are present in the final resin). Tertiary aminegroups are excellent catalysts for the isocyanate crosslinking reactionused to cure compositions of this invention.

Preferred hydroxy functional epoxy ester resins of the invention includesignificant aromatic content which is believed to enhance corrosionresistance properties. Even though aromatics tend to increase thebrittleness of cured compositions including such resins, it is possibleto include them since, as mentioned above, the polycaprolactone diolportions of the cured composition gives the cured composition increasedflexibility which can more than compensate for such brittleness. Aparticularly preferred embodiment of the hydroxy functional epoxy esterresin of the invention is prepared from aromatic containing diepoxidewhich is extended with diphenol and dicarboxylic acid. In addition, itis presently understood that the phenolic oxygens introduced into theepoxy ester resin by the chain extension reaction of epoxy with phenol,advantageously provide excellent adhesion to metal substrates, forexample steel.

According to a most preferred embodiment of the invention, furtherdiscussed below, acyclic aliphatic dicarboxylic acid is employed in thechain extension of the diepoxide. According to this embodiment, theepoxy ester resin reaction product comprises both aromatic and aliphaticmoieties in random sequence and distribution. While, not wishing to bebound by theory, it is presently understood that the aromatic units ofthe diphenol and the aliphatic units of the dicarboxylic units eachenhance the advantages of the other in an unexpected and synergisticmanner. More specifically, the aliphatic units are seen to provideflexibility to the epoxy ester resin while the aromatic units, asmentioned above, provide moisture and corrosion resistance. Thus, theepoxy ester resin of the composition makes a significant contribution toformulation of a coating having both good flexibility and good moistureand corrosion resistance.

Each of the above major components of the compositions as well as othercomponents and other aspects of the invention are described hereinafterin greater detail.

A. Hydroxy Functional Epoxy Ester Resin

As described above, this resin is formed by reacting chain extendeddiepoxide with hydroxy functional secondary amine in chain terminatingreaction. The chain extended diepoxide is prepared by reacting diphenoland dicarboxylic acid substantially simultaneously with diepoxide inchain extension reaction.

Each of the reactants employed in the preparation of the hydroxyfunctional epoxy ester resin is described in greater detail below.

(i) Diepoxide Reactant

The chain extended diepoxide reactant employed in the manufacture of thehydroxy functional epoxy ester resin is prepared by substantiallysimultaneous chain extension of diepoxide with dicarboxylic acid anddiphenol. While, ultimately, the choice of dicarboxylic acid/diphenolextended diepoxide reactant for preparing the epoxy ester resin willdepend to an extent upon the particular application intended for thecoating composition, terminal diepoxides, that is chain extendeddiepoxides bearing two terminal epoxide groups, are generally mostpreferred. These are generally more reactive and therefore requirereaction conditions under which undesirable side reactions, for example,epoxy-epoxy reactions and gellation, can be more easily avoided.Preferably, the chain extended diepoxide has a number average molecularweight (Mn) between about 1,200 and about 3,500, and more preferablybetween about 1,600 and about 2,400. The diepoxides which are to bechain extended with dicarboxylic acid and diphenol may be selected fromnumerous diepoxides, some of which may be diphenol extended diepoxides.

Numerous diepoxides previously extended with diphenol are commerciallyavailable. These include certain of the well known bisphenol-Aepichlorohydrin epoxy resins of the Epon (trademark) series, ShellChemical Company, Houston, Tex., e.g., Epon 1001 and Epon 1004 and theDER (trademark) series, Dow Chemical Company, Midland, Mich., e.g., DER332. These diglycidyl ether bisphenol-A resins, or high molecular weightanalogs thereof, are preferred in view of their cost and commercialavailability.

Other suitable diepoxy resins, not previously extended with diphenol,may be extended with dicarboxylic acid and diphenol and used in thepreparation of the hydroxy functional epoxy ester resin. Preferreddiepoxy resins of this type include Epon 828 (trademark) and Epon 829(trademark), which are non-extended diepoxides of the aforementionedEpon Series, as well as cycloaliphatic diepoxy resins, such as theEponex (trademark) series, Shell Chemical Company; hydantoin epoxyresins such as, for example, Resin XB2793 (trademark), Ciba-GeigyCorporation, Ardsley, N.Y.; and any of a wide variety of acyclic orcyclic aliphatic diepoxides such as, for example, 1,4-butanedioldiglycidyl ether and 4-vinyl-cyclohexene dioxide and the like.

Still other suitable diepoxides which may be chain extended withdicarboxylic acid and diphenol and used in synthesizing the epoxy esterresin are commercially available and will be apparent to the skilled ofthe art in view of the present disclosure. Also, it will be understoodfrom the foregoing that any mixture of compatible diepoxides may beused.

In addition to the diphenol and dicarboxylic acid chain extendeddiepoxide, a portion of the epoxide functionality can be provided by anycompatible monoepoxy compound or polyepoxy compound (which may bediphenol and dicarboxylic acid chain extended) or mixture of suchcompounds. The polyepoxide can be any of the well known types such aspolyglycidyl ethers of polyphenols. These can be produced byetherification of polyphenol with epihalohydrin in the presence ofalkali. It will be recognized by the skilled of the art in view of thepresent disclosure, that in some instances, particularly where a coatingcomposition of high solids content is less important, it may bedesirable to incorporate polyepoxide of higher molecular weight.Preferably, any such polyepoxide contains free hydroxyl groups inaddition to epoxide groups. While polyglycidyl ethers of polyphenol canbe employed, it may be desirable to react a portion of the reactivesites (hydroxy or in some instances epoxy) with a modifying material tovary the film characteristics of the epoxy resin. The epoxy resin may bemodified, for example, with isocyanate group containing organicmaterials or other reactive organic materials. Other useful polyepoxidesare the novolak resins including, for example, the novolak epoxy resinsECN 1235 (trademark) and ECN 1273 (trademark), Ciba-Geigy Corporation.According to preferred embodiments of the present invention, epoxidecompounds other than diepoxide compounds provide no more than about 15%and most preferably substantially none of the total epoxidefunctionality in the reactants used to form the epoxy ester resin.

(ii) Diphenol Reactant

The diphenol reactants suitable for reaction with the diepoxide reactantand dicarboxylic acid in chain extension reaction include numerouscommercially available materials, many of which will be readily apparentto the skilled of the art in view of the present disclosure. Preferreddiphenols have the general formula (I): ##STR1## wherein R is a divalentlinking moiety substantially unreactive with the diepoxide resin.Preferably R is a divalent organic linking moiety, for example (CH₂)_(n)where n is preferably from about 1 to about 8, C═O, and the like,although inorganic moieties, for example sulfonyl and the like, are alsosuitable. Diphenols of this character have been found to provide goodreactivity with diepoxides described above and to provide, ultimately,cured coatings of the invention having excellent physical properties,most notably excellent corrosion protection. It will be apparent to theskilled of the art in view of the present disclosure that R should besubstantially unreactive with the hydroxy functional secondary amineemployed in preparation of the hydroxy functional epoxy ester resin.Particularly preferred diphenols include those according to formula (I)above, wherein R is selected from the group comprising a straight orbranched alkylene or alkylidene moiety of one to about 10 carbons,preferably having three to four carbons and most preferably having thegeneral formula: ##STR2## wherein R' and R" are the same or differentand each is a monovalent organic moiety preferrably selected from thegroup comprising hydrogen and lower alkyl of about one to four carbons,most preferably one or two carbons, and the like or a mixture of any ofthem. Preferably the diphenol has a number average molecular weight (Mn)between about 180 and about 500, more preferably between about 180 andabout 250. Such diphenols include, for example bisphenol-A, which ismost preferred, bisphenol-B, bisphenol-F and the like and a compatiblemixture of any of them. As used herein the term diphenol may include,for example, compounds comprising a single dihydroxy substituted phenylring such as benzenediol. More preferred, however, are those diphenolsproviding two terminal, monohydroxy substituted phenyl rings such as informula (I), above. Other examples of diphenols arebis-(4-hydroxy-tertbutylphenyl)-2,2-propane,bis-(2-hydroxy-naphthyl)-methane and 1,5-dihydroxynaphthalene. Othersuitable diphenols for preparation of the epoxy ester resin of thepresent invention will be apparent to the skilled of the art in view ofthe present disclosure.

(iii) Dicarboxylic Acid Reactant

Dicarboxylic acids suitable for chain extended diepoxides along withdiphenol preferably have a number average molecular weight of betweenabout 145 and about 1000 and most preferably between about 400 and about600. Suitable dicarboxylic acids include numerous commercially availablematerials, many of which will be readily apparent to the skilled of theart in view of the present disclosure. Suitable dicarboxylic acidsinclude saturated or unsaturated, cyclic or acyclic, aliphatic oraromatic dicarboxylic acids or a mixture thereof. Acyclic aliphaticdicarboxylic acids are generally preferred in view of the enhancedflexibility they provide to the cured coatings of the invention.Preferred dicarboxylic acids have the general formula (I):

    HOOC--R"'--COOH                                            (I)

wherein R"' is a divalent linking moiety substantially unreactive withthe diepoxide resin. It will be apparent to the skilled of the art inview of the present disclosure, that R"' should be substantiallyunreactive also with the hydroxy functional secondary amine employed inpreparation of the epoxy ester resin and with hydroxy functionality(generated in the chain-extension reaction). Preferably R"' is adivalent, organic linking moiety. Particularly preferred are thosedicarboxylic acids wherein R" is selected, from the group comprising astraight or branched alkylene or alkylidene moiety, preferably of about4-42 carbons, for example, (CH₂)_(n) where n is preferably from about 4to about 42, and the like or mixtures thereof. Dicarboxylic acids ofthis character have been found to provide good reactivity with thepreferred diepoxides described above and to provide, ultimately, curedcoatings of the invention having excellent physical properties, mostnotably excellent flexibility and corrosion protection.

Exemplary dicarboxylic acids include adipic acid,3,3-dimethylpentanedioic acid, benzenedicarboxylic acid,phenylenediethanoic acid, naphthalenedicarboxylic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, and the like or a compatiblemixture of any of them. While dicarboxylic acids according to formula(I) can be used, wherein R"' is an alkylene chain of less than 4carbons, for example, oxalic acid, malonic acid, succinic acid, glutaricacid and the like, these are less preferred in view of the somewhatlesser degree of flexibility provided thereby. Preferably thedicarboxylic acid provides two terminal carboxyl groups. Similarly,preferred aromatic dicarboxylic acids are those wherein the carboxylicgroups are more spaced apart, for example, 1,4-benzenedicarboxlyic acidand 2,7-naphthalene-dicarboxylic acid.

The most preferred dicarboxylic acids are substantailly saturated,acyclic, aliphatic dimer acids, which are well known to the skilled ofthe art and readily commercially available. These are typically thedimerization reaction products of fatty acids which have from 4 to 22carbons and a terminal carboxyl group. Of these, dimer acid of 36carbons is most prefered since it provides excellent reactivity with thepreferred diepoxides described above, provides epoxy ester reactionproducts of advantageously wide molecular weight distribution, andprovides, ultimately, cured coatings of the invention having excellentphyscial properties. In addition, dimer acid of 36 carbons is readilycommercially available, for example, as Empol 1014 (trademark), Empol1016 (trademark) and Empol 1018 (trademark), each available from EmeryIndustries, Inc., Cincinnati, Ohio. It should be recognized that most orall commercially available dimer acids contain some portion of trimeracid, typically, for example, about 5-10% but in some case as much as30% or more, and also contain a usually smaller portion ofmonocarboxylic acid. As used herein, the term "dimer acid" includesthose containing such amounts of these materials. Most useful in thepresent compositions are products that contain mostly dibasic acid andnone or low amounts of tribasic and monobasic acids.

Aliphatic dicarboxylic acids are seen to provide additional advantages.In particular, while not wishing to be bound by theory, it is presentlyunderstood that epoxy ester resins derived therefrom wet the substratesurface better and, thus, provide enhanced adhesion between thesubstrate and the cured coating. They also flow better and provide anexcellent, smooth surface upon being cured. Also, the aliphatic unitsprovide enhanced flexibility to the cured coating, as noted above, andthis flexibility of the coating is seen to provide enhanced impactresistance as does the polycaprolactone portion of the cured coating.

Where corrosion protection for the substrate is important, it may bepreferred to employ dicarboxylic acid according to formula (I) above,wherein R"' is, at least in part, aromatic. As noted above, it isbelieved that aromatics in a coating composition of the invention, suchas a primer composition for a metal substrate, are more resistant tohydrolysis than are aliphatics and, therefore, provide enhancedcorrosion and moisture resistance. Of course, the diphenol and,according to preferred embodiments described above, the diepoxidereactant each provides aromatic units to the resin and each wouldsimilarly contribute to corrosion and moisture resistance.

Other suitable dicarboxylic acids for preparation of the epoxy esterresin of the present invention will be apparent to the skilled of theart in view of the present disclosure.

(iv) Hydroxy Functional Secondary Amine Reactant

The hydroxy functional secondary amine which is reacted in chainterminating reaction with the reaction product of the above describeddiepoxide, diphenol and dicarboxylic acid may be selected from a broadclass of aliphatic, cycloaliphatic and aromatic hydroxy functonalamines.

Numerous such amines, which may bear mono- or dihydroxy functionalitywill be apparent to those skilled in the art in view of the presentdisclosure. Exemplary of such amines are those having the formula (II):##STR3## wherein R and R' are selected from the group consisting ofaliphatic, cycloaliphatic and aromatic radicals which will not interferewith the chain termination reaction between the chain extended diepoxideand the hydroxy functional secondary amine. R and R' in the aboveformula may be the same or different, but preferably should be of thesame nature. X may be selected from hydrogen and hydroxyl radical.

While the hydroxyl group on R and/or R' may be other than primary,primary hydroxyls are preferred since such primary hydroxyl groups aremore reactive (i.e., they react faster) with the polyisocyanatecrosslinking agent of the composition during curing.

Examples of preferred radicals R and R' for the hydroxy functional amineof the above formula are: ##STR4## Preferably R and R' are methylene,ethylene, or lower alkylene groups but they may be any othernoninterfering radical including those, for example, such as benzyl,oxyalkylene, etc.

Particularly preferred primary hydroxy bearing amines for use inpreparing the hydroxy functional epoxy ester resin are diethanol amine,methylethanol amine, dipropanol amine and methylpropanol amine.

The hydroxy functional epoxy ester resin of the invention can be madeaccording to reaction conditions now specified employing techniqueswhich are well known and which will be readily apparent to the skilledof the art in view of the present disclosure. The chain extension andchain termination reactions occur sequentially, with the chain extensionof the diepoxide being carried out first. Diepoxide, diphenol anddicarboxylic acid are charged into a suitable reactor and heated. Thereactants are used in relative proportions to yield a chain extensionreaction product bearing two unreacted epoxy groups and preferablysubstantially no unreacted carboxyl or phenol functionality. Suitableseparation techniques are known to the skilled of the art for removal ofunused reactants. It should be recognized that to assure rapid and/ormore complete reaction of the diepoxide with the phenol and dicarboxylicacid functionality, it is usually preferred to have a catalyst present.The use of catalyst has been found to provide advantageous hydroxyfunctional epoxy ester resin of the invention and is preferred. Epon 829(trademark), mentioned above, as sold, provides a proprietary catalyst.Epon 828 (trademark), is substantially the same but does not providesuch catalyst. Suitable catalysts are commerically available and includeany of the well known catalysts for epoxy-phenol and epoxy-carboxylicacid reactions such as, for example, sodium carbonate andformylmethyltriphenylphosphonium chloride which are preferred, andlithium neodecanoate, lithium naphthenate, lithium nanoate, other knownorganometallic catalysts and tertiary amine catalysts and the like or acompatible mixture of any of them. Still other suitable catalysts aredescribed in U.S. Pat. Nos. 4,389,520 and 3,477,990. Others will beapparent to the skilled of the art in view of the present disclosure.

The reaction mixture is heated to at least about 135° C. (280° F.). Whenin the presence of catalyst, exothermic reaction will proceed with orwithout further heating. Typically, the reaction mixture will then readabout 170° C.-190° C. (340° F.-370° F.), depending upon the batch sizeand reactor vessel insulation, ect. In the absence of catalyst, suchexotherm is typically not observed and continued heating is required.The progress of the reaction can be followed by measuring acid numberand/or weight per epoxide (WPE), i.e., epoxy equivalent weight.

As noted above the diepoxide is reacted substantially simultaneouslywith diphenol and dicarboxylic acid in amounts sufficient to give aweight per epoxide (WPE) of between about 500 and about 2,500,preferably between about 500 and about 1,500. Preferably, the acid anddiphenol reacted with the diepoxide are employed in a ratio of 10/90 to90/10.

After completion of the above chain extension reaction the hydroxyfunctional secondary amine reactant is charged into the reaction vessel.The reaction is exothermic and drives itself to completion.

As noted above, the chain extended reacton product is reacted with thehydroxy functional secondary amine in chain terminating reaction inapproximately 1 to 1 equivalent ratio, i.e., in approximately 1 to 1equivalent ratio of epoxide groups to amine groups. This ratio isdesireable since excess epoxy could result in gelation of the reactionmixture while excess amine remaining in the reaction mixture could reactwith some of the polyisocyanate crosslinking agent in the composition,which would then not be available for curing the coating compositionresin. For this reason, if excess amine is used during formation of theprecursor, it should preferably be removed prior to reaction of theprecursor with lactone monomers.

(B) Linear Polycaprolactone Diol

The linear polycaprolactone diol employed in the coating composition ofthe present invention has a molecular weight of between about 1500 andabout 5000, preferably between about 2000 and about 4000. Numeroussuitable polycaprolactone diols will be apparent to the skilled in theart in view of the present disclosure and include, for example, thoseformed by polymerizing lactones in the presence of an initiator bymethods well known to those skilled in the art. Suitable linearpolycaprolactone diols also are commercially available, for example,from Union Carbide, Danbury, Conn. as the TONE (trademark) Series, e.g.,TONE 0260. This series comprises polycaprolactone diols as well aspolycaprolactone triols.

The preparation of suitable polycaprolactone diols is described, forexample, in U.S. Pat. Nos. 2,914,556 and 3,169,945 to Hostettler et al.Polymerization of the lactone monomer to form the polycaprolatone diolof this invention is initiated by reaction with one or more compoundshaving two functional groups each having an active hydrogen capable,with or without the aid of a catalyst, of opening the lactone ring andadding it as an open chain without forming water of condensation.Compounds suitable for use to initiate the polymerization of thelactones, referred to herein as initiators, include, but are not limitedto, diamines, diols, amino alcohols, diacids, hydroxy-carboxylic acids.Also suitable are amides. sulfonamides, hydrozones, carbazone, oximesand vinyl polymers containing two reactive groups. The lactone startingmaterial which may be employed in forming the polycaprolactone diolcomponent of the invention may be any lactone, or combination oflactones, having at least six carbon atoms, for example, from six toeight carbon atoms, in the ring and at least one hydrogen substituent onthe carbon atom which is attached to the oxy group in said ring. In oneaspect, the lactone used as a starting material can be represented bythe general formula: ##STR5## in which n is at least four, for example,from four to six, at least n+2R's are hydrogen, and the remaining R'sare substituents selected from the group consisting of hydrogen, alkyl,cycloalkyl, alkoxy and single ring aromatic hydrocarbon radicals.Lactones having greater numbers of substituents other than hydrogen onthe ring, and lactones having five or less carbon atoms in the ring, areconsidered unsuitable for the purposes of the invention because of thetendency that polymers thereof have to revert to the monomer,particularly at elevated temperature.

The lactones preferred in this invention for forming thepolycaprolactone diol are the epsilon-caprolactones having the generalformula: ##STR6## wherein at least six of the R's are hydrogen and theremainder are hydrogen, alkyl, cycloalkyl, alkoxy or single ringaromatic hydrocarbon radicals, none of the substituents contain morethan about twelve carbon atoms, and the total number of carbon atoms inthe substituents on a lactone ring does not exceed about twelve.Unsubstituted epsilon-caprolactone, in which all the R's are hydrogen,is derived from 6-hydroxyhexanoic acid and is most preferred.Substituted epsilon-caprolactones, and mixtures thereof, are availableby reacting a corresponding substituted cyclohexanone with an oxidizingagent such as peracetic acid.

Among the substituted epsilon-caprolactones considered most suitable forthe purposes of the invention are the various monoalkylepsilon-caprolactones such as the monomethyl-, monoethyl-, monopropyl-,monoisopropyl-, etc. to monododecyl epsilon-caprolactones; dialkylepsilon-caprolactones in which the two alkyl groups are substituted onthe same or different carbon atoms, but not both on the epsilon carbonatom; trialkyl epsilon-caprolactones in which two or three carbon atomsin the lactone ring are substituted, so long as the epsilon carbon atomis not disubstituted alkoxy epsilon-caprolactones such as methoxy andethoxy epsilon-caprolactones; and cycloalkyl, aryl, and aralkylepsilon-caprolactones such as cyclohexyl, phenyl and benzylepsilon-caprolactones.

Lactones having more than six carbon atoms in the ring, e.g.,zeta-enatholactone and eta-caprylolactone may also be polymerized toform the linear polycaprolactone diol employed in the invention.

Diols that are suitable as bifunctional

initiators include glycols of the formula HO(CH₂)_(n) OH in which nequals 2 to 10, glycols of the formula HO(CH₂ CH₂ O)_(n) H and HO(CHCH₃CH₂₀ O)_(n) H in which n equals 1 to 40, such as ethylene glycol,diethylene glycol, and the like, 2,2-dimethyl-1,3-propanediol,2,2-diethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, N-methyl andN-ethyl diethanol amines, various cyclohexanediols such as4,4'-methylenebiscyclohexanol, 4,4'-isopropylidenebiscyclohexanol,various xylenediols, various hydroxymethyl-phenethyl alcohols, varioushydroxy-methyl-phenyldipropanols, various phenylenediethanols, variousphenyldipropanols, and various heterocyclic diols such as1,4-piperazinediethanol. Other suitable diols include polyoxyalkylatedderivatives of difunctional compounds having two reactive hydrogenatoms. These difunctional compounds may contain primary or secondaryhydroxyls, phenolic hydroxyls, primary or secondary amino groups, amido,hydrazino, guanido, ureido, mercapto, sulfino, sulfonamide, or carboxylgroups. They are obtainable by reacting diols of the class HO(CH₂)_(n)OH, wherein n equals 2 to 10, propylene glycol, thiodiethanol,xylenediols, 4,4'-methylenediphenol, 4,4'-isopropylidenediphenol, andresorcinol; mercapto alcohols, like mercaptoethanol; dibasic acids, suchas maleic, succinic, glutaric, adipic, pimelic, sebacic, phthalic,tetrahydrophthalic, and hexahydrophthalic; phosphorous acid; aliphatic,aromatic and cycloaliphatic primary monoamines, like methylamine,ethylamine, propylamine, butylamine, aniline, cyclohexylamine; secondarydiamines, like N,N'-dimethylethylenediamine; and amino alcoholscontaining a secondary amino group, like N-methylethanolamine, withalkylene oxides such as ethylene oxide, propylene oxide, 1-butyleneoxide, 2-butylene oxide, isobutylene oxide, butadiene monooxide, styreneoxide, and also mixtures of these monoepoxides.

Other useful bifunctional initiators are polymers of monoepoxidesobtainable by polymerizing with such catalyst as oxonium salts ofhydrogen halides; metal or nonmetal halides whose etherates are oxoniumcomplexes; electrophilic metal or non-metal halides in the presence ofhydrogen halides, acyl halides, or anhydrides of inorganic and organicacids; and inorganic acids or anhydrides thereof whose anions showlittle tendency to polarize. Polymers containing hydroxyl end groups canbe obtained by treating these products with alkaline reagents uponcompletion of the polymerization reaction. Among suitable monoepoxidesfor preparing such polymers are tetrahydrofuran, trimethylene oxide,propylene oxide, ethylene oxide and mixtures thereof.

Difunctional amino alcohols capable of initiating the polymerization oflactones include aliphatic amino alcohols of the general formulaHO(CH₂)_(n) NH₂, wherein n equals 2 to 10, N-methylethanolamine,isopropanolamine N-methylisopropanolamine, aromatic amino alcohols likepara-amino-phenethyl alcohol, and para-amino-alphamethylbenzyl alcohol,and various cycloaliphatic amino alcohols like 4-amino-cyclohexanol.

Suitable diamines include aliphatic diamines of the general formula H₂N(CH₂)_(n) NH₂ ; monosecondary diamines of the general formulaR"NH(CH₂)_(n) NH₂ ; disecondary diamines of the general formulaR"NH(CH₂)_(n) NHR", where n equals 2 to 10 and where R" is alkyl, aryl,aralkyl or cycloalkyl; aromatic diamines, like metaphenylenediamine,para-phenylenediamine, toluene2,4-diamine, toluene-2,6-diamine,1,5-naphthalenediamine, 1,8-naphthalenediamine, meta-xylylenediamine,para-xylylenediamine, benzidine, 3,3'-dimethyl-4,4'-biphenyldiamine,3,3'-dimethoxy-4,4'-bi-phenyldiamine,3,3'-dichloro-4,4'-biphenyldiamine, 4,4'-methylenedianiline,4,4'-ethylenedianiline, 2,3,5,6,-tetramethyl-para-phenylenediamine,2,5-fluorenediamine, and 2,7-fluorenediamine; cycloaliphatic diamineslike 1,4-cyclohexanediamine, 4,4'-methylenebiscyclohexylamine, and4,4'-isopropylidenebiscyclohexylamine; and heterocyclic amines such aspiperazine, 2,5-dimethylpiperazine, and 1,4-bis(3-aminopropyl)piperazine

Representatives of the many dicarboxylic acids that are suitable asbifunctional initiators are such dicarboxylic acids as oxalic acid,succinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, 4,4'-oxydibutyric acid,5,5'-oxydivaleric acid, 6,6'-oxydihexanoic acid, 4,4'-thiodibutyricacid, 5,5'-thiodivaleric acid, 6,6'-thiodihexanoic acid, itaconic acid,phthalic acid, isophthalic acid, terephthalic acid, 1,5-naphthoic acid,2,7-naphthoic acid, 2,6-naphthoic acid, 3,3'-methylenedibenzoic acid,various tetrahydrophthalic acids, and various hexahydrophthalic acids.Suitable hydroxy- and aminocarboxylic acids include -hydroxypropionicacid, 6-hydroxycaproic acid, 1-hydroxy-undecanoic acid, salicylic acid,parahydroxybenzoic acid, beta-alanine, 6-aminocaproic acid,7-aminoheptanoic acid, 11-amino-undecanoic acid, and paraaminobenzoicacid.

The initiator is believed to open the lactone ring to produce an esteror amide having two terminal groups that are capable of opening furtherlactone rings and thereby of adding more and more lactone to themolecule. Thus, for example, the polymerization of epsilon-caprolactoneinitiated with a diol is believed to take place primarily as follows:##STR7## wherein a is the total number of mols of lactone reacted permol of initiator and b+c=a.

To initiate and continue the polymerization of the lactone, the lactoneand the initiator are preferably heated to a temperature between about130° and 200°C. In order to achieve a practical and desirable rate ofreaction with a minimum of decompensation. The temperature may beconsiderably lower however, i.e., as low as about 50°C. at the sacrificeof speed of reaction. It may also be considerably higher, i.e., up toabout 300°C., although care must be taken at such higher temperaturesbecause of the more likely losses, at temperatures about 250°C., due todecompensation or undesirable side reactions. Generally, therefore, atemperature range of 50° to 300°C. is considered operable and a morelimited range between about 130° and 200°C. is considered preferable.

It is within the ability of the skilled in the art to determine asuitable amount of initiator to use to achieve a linear polycaprolactonediol of desired molecular weight. The polymerization may be, andpreferably is, carried out with the use of a catalyst, such as a basicor neutral ester interchange catalyst, to accelerate the reaction. Amongcatalysts suitable for this purpose are such metals as lithium, sodium,potassium, rubidium, cesium, magnesium, calcium, barium, strontium,zinc, aluminum, titanium, cobalt, germanium, tin, lead, antimony,arsenic and cerium, as well as the alkoxides thereof. Additionalsuitable catalysts are, by way of example, the carbonates of alkali- andalkaline earth metals, zinc borate, lead borate, zinc oxide, leadsilicate, lead arsenate, litharge, lead carbonate, antimony trioxide,germanium dioxide, cerium trioxide, cobaltous acetate and aluminumisopropoxide. Catalyst concentrations between about 0.001 and 0.5%,based on the weight of the starting lactones, are suitable. Thepreferred range is from 0.01 to 0.2%.

While not wishing to be bound by theory, it is presently understood thatthe linear polycaprolactone diol is characterized by the presence ofseries of interconnected, substantially linear units or groups composedof carbon, hydrogen and oxygen. The interconnected units are openedlactone residues each having a terminal oxy group at one end, a carbonylgroup at the other end, an intermediate chain of at least five carbonatoms and at least one hydrogen substituent on the carbon atom in theintermediate chain that is attached to the terminal oxy group. The oxygroup of one lactone residue is connected to the carbonyl group of anadjacent lactone residue in the series and the oxy group of the lastlactone residue in a series is connected to a hydrogen to form aterminal hydroxyl group at the end of the series.

The hydroxy functional epoxy ester resin and the linear polycaprolactonediol are included in the coating composition in a weight ratio ofbetween about 1:4 and 4:1, preferably in a weight ratio of about 1:1.

C. Blocked Polyisocyanate Crosslinking Agent

The crosslinking agent employed in the novel solvent based coatingcompositions of the invention comprises blocked polyisocyanate. Thenovel solvent based coating compositions of the invention, as a resultof employing blocked polyisocyanate crosslinking agents, exhibitexceptional shelf stability even when corrosion inhibiting pigments suchas zinc chromate are used in high concentrations.

As used herein "blocked polyisocyanate" means an isocyanate compoundcontaining two or more isocyanate groups, all of which have been reactedwith a material which will prevent reaction of the isocyanate group atroom temperature with compounds that conventionally react with suchgroups, and at least some of which will permit that reaction to occur athigher (cure) temperatures. In general the blocked polyisocyanate may beprepared by reacting a sufficient quantity of an active hydrogencontaining blocking agent with the polyisocyanate to insure that no freeisocyanato groups are present. The blocking agent may be represented bythe formula BH and may be selected from numerous materials, hereinafterdiscussed, which bear an active hydrogen.

The blocked polyisocyanate crosslinking agent is included incompositions of the invention in an amount equal to between about 10 andabout 50 percent, preferably in an amount equal to between about 20 andabout 40 percent, of the combined weight of hydroxy functional epoxyester resin (A) and linear-polycaprolactone diol (B) in the composition.The blocked crosslinking agent de-blocks at the cure temperature of thecoating composition.

Blocked polyisocyanates of numerous types may be employed in thecompositions of the invention. Particularly suitable blockedpolyisocyanates, which will be discussed further hereinafter, includeblocked polymethylene polyphenol isocyanates, isocyanurate ringcontaining blocked polyisocyanates and certain oligoester modifiedblocked polyisocyanates.

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examples arethe aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidine and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4'4"-triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5-tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; trimethylolpropane, pentaerythritol, andthe like, as well as mono-ethers such as diethylene glycol, tripropyleneglycol and the like and polyethers, i.e., alkylene oxide condensates ofthe above. Among the alkylene oxides that may be condensed with thesepolyols to form polyethers are ethylene oxide, propylene oxide, butyleneoxide, styrene oxide and the like. These are generally calledhydroxyl-terminated polyethers and can be linear or branched. Examplesof polyethers include polyoxyethylene glycol, polyoxypropylene glycol,polyoxytetramethylene glycol, polyoxyhexamethylene glycol,polyoxynonamethylene glycol, polyoxydecamethylene glycol,polyoxydodecamethylene glycol and mixtures thereof. Other types ofpolyoxyalkylene glycol ethers can be used. Especially useful polyetherpolyols are those derived from reacting polyols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,3-butyleneglycol, 1,6-hexanediol, and their mixtures; glycerol, trimethylolethane,trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol,methyl glucosides, sucrose and the like with alkylene oxides such asethylene oxide, propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR8##wherein n equals 1 to 3. Such compounds, sold under the tradename "PAPI"by the Upjohn Chemical Company of Kalamazoo, Mich., have proven to beparticularly useful in compositions of the invention, resulting incompositions exhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Representative of those blocking agents which are preferred are thoseselected from the group consisting of (i) aliphatic, cycloaliphatic andaromatic alkyl monoalcohols; (ii) hydroxyl amines; (iii) oximes; (iv)lactams; and (v) triazoles. Any suitable aliphatic, cycloaliphatic oraromatic alkyl monoalcohol may be used as a blocking agent in accordancewith the present invention. For example, aliphatic alcohols, such asmethyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl,nonyl, 3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the likemay be employed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are epsilon-caprolactam,epsilon-butyrolactam and pyrrolidone, while suitable triazoles includecompounds such as 1,2,4-triazole, 1,2,3-benzotriazole, 1,2,3-tolyltriazole and 4,5-diphenyl-1,2,3-triazole. Particularly preferred activehydrogen containing blocking agents are methylethyl ketoxime and2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class type of blocked polyisocyanatecrosslinking agent which may be employed in the novel solvent basedcoating compositions of the invention comprises isoycanurate ringcontaining blocked isocyanate compounds. In general, these blockedpolyisocyanates may be formed by blocking with the aforementionedblocking agent isocyanurate ring containing polyisocyanates. Thesecompounds may be formed by cyclotrimerization of difunctionalisocyanates. Usually, the reaction does not stop in this stage andcontinues through the formation of polyfunctional oligomers or a mixtureof such oligomers with a portion of the pure trifunctionalpolyisocyanate. Mixtures of trifunctional product and variouspolyfunctional oligomers are commercially available.

A particular desirable blocked polyisocyanate crosslinking agent is theblocked form of the pure trifunctional isocyanurate represented by thefollowing formula: ##STR9## wherein R is selected from the groupconsisting of aliphatic, cycloaliphatic and aromatic groups andcombinations thereof and B is the residue of an active hydrogencontaining blocking agent. More specifically, this compound is disclosedin U.S. Pat. No. 4,491,663, the disclosure of which is incorporatedherein by reference.

(ii) Oligoester Modified Blocked Polyisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the novel solvent based coating compositions of this inventionare oligoester modified blocked polyisocyanates prepared from aparticular class of oligoester diols and triols. A first type of sucholigoester modified blocked polyisocyanates is prepared from organicdiisocyanates bearing one isocyanate group more reactive than the other,with the more reactive isocyanate first being blocked with a blockingagent and the remaining isocyanate group then being reacted withhydroxyl functionality of an oligoester diol or triol as referred toabove. The second type of oligoester modified blocked polyisocyanate maybe prepared by reacting oligoester diols from the aforementioned classof oligoesters with an excess of organic diisocyanate so as to form anisocyanate terminated prepolymer followed by blocking of the terminalisocyanate groups of the prepolymer with an active hydrogen containingblocking agent. Each of these materials is particularly useful in thecompositions of the invention and produces final cured coatingcompositions exhibiting outstanding flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issuedMarch 30, 1982, the disclosure of which is hereby incorporated byreference. The hydroxy functional oligoesters within the useful class ofmaterials (i) have a number average molecular weight (Mn) between about150 and about 3000, preferably between about 230 and about 1000, (ii)bear 2 or 3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide;

(b) the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and mono-or polyepoxide, preferably monoepoxide; (d) theesterification reaction product of monocarboxylic acid and hydroxyfunctional mono- or polyepoxide, preferably monoepoxide; and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanate group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveisocyanate groups, thus providing a half-blocked diisocyanate and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate crosslinking agents useful in compositionsof the invention. The organic polyisocyanate-blocking agent adductintermediate is formed by reacting a sufficient quantity of the blockingagent with the organic diisocyanate to insure that one of the two --NCOgroups on the diisocyanate is reacted. The reaction between the organicdiisocyanate and the blocking agent is exothermic; therefore, thediisocyanate and the blocking agent are preferably admixed attemperatures no higher than about 80°C., preferably below about 50°C.,to minimize the exothermic effect.

This intermediate is next reacted with the oligoester diol or trioldescribed above so as to react substantially all free or unblockedisocyanato groups of the diisocyanate/blocking agent intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80° -120°C..

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate with an oligoester diol from the above describedclass of oligoesters followed by reaction of the terminal isocyanategroups formed on the resulant prepolymer with an active hydrogencontaining blocking agent as described above so as to react withsubstantially all the isocyanate groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanate group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

D. General Discussion --Other Aspects of Invention and Other Components

The coating compositions of the invention have been found to provide acured coating having the advantageous physical properties describedabove, over a wide range of cure temperatures and a wide range of solidslevels. More specifically, the coating compositions according topreferred embodiments of the invention have been found to cure attemperatures from as low as about 120°C. or less within about 15 minutesor less, and yet to cure and suffer no significant loss of advantageousphysical properties at temperatures as high as about 200°C. or more forperiods up to about 60 minutes or more. Considered together with thestorage stability of the coating composition, it can be readilyrecognized that the present invention provides a highly significantadvance in the coating composition art.

It will be within the skill of the art to determine the proper volatileorganic content for a given coating composition of the invention and fora given application. Preferred solvents have relatively low volatilityat temperatures appreciably below their boiling points such that solventevaporation is low during storage and/or application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in con3unction with it during the curing porcess orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for application to the substrate in thedesired manner.

Obviously, in those cases where the composition is to be applied as achip resistant primer the amount of solvent will be reduced so as togive a solids level of about 65-80%. Such higher solids materials aregenerally applied using hot spray equipment.

Flow control agent(s), for example, polybutyl acrylate; wettingagent(s), for example, silicone; pigments; pigment dispersants;corrosion inhibitors, for example, chromate pigments, numerous of all ofwhich are known to the skilled of the art, may be employed in thecoating compositions of the invention. In addition, suitable reactiveadditives can be used, including, for example, low molecular weight diolflow control agents and reactive diluents.

Compositions of the invention, and in particular the chip resistantprimers of the invention, may also include anti-settling or anti-saggingagents to control the thixotropic properties of the composition.Exemplary of available materials suitable for this purpose are Dislon(trademark) 6900-20X manufactured by Kusumoto Chemicals, Ltd., Tokyo,Japan and sold by Kind Inudstries, Norwalk, CT. 06852; Bentone(trademark) 38, N. L. Industries, Highstown, N.J. 08520 and Cab-O-Sil(trademark) M-5, Cabot Corporation.

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe hydroxyl functionality of the epoxy ester resin and linearpolycaprolactone diol. The time and temperature required to cure thecoating are interrelated and depend upon the particular epoxy esterresin, polycaprolactone diol, crosslinking agent, solvent and othermaterials, if any, and the amount of each comprising the coatingcomposition. The coating compositions according to preferred embodimentsof the invention, as described above, have been found to provide thebest coating results when cured at temperature at about 150°C. (300°F.)for 20 minutes. It is a highly significant advantage of the invention,however, that these same coating compositions can withstand, forexample, temperature as high as about 200°C. (390°F.) for periods oftime as long as about 60 minutes. Accordingly, great flexibility isprovided in both designing and implementing a curing schedule for partscoated with the coating compositions of the invention. Thus, in theassembly of automotive vehicles, for example, vehicles unavoidably heldin a curing oven for long periods of time during unplanned assembly lineshut-downs are recovered with cured and unharmed coatings.

High solids coating compositions according to the present invention,comprising the crosslinkable epoxy ester resins of the invention,especially the preferred resins described above, the linearpolycaprolactone diol, especially the preferred polycaprolactone dioldescribed above, and blocked polyisocyanate crosslinking agent,especially the preferred materials described above have been found toafford cured coatings with improved corrosion resistance and chipresistance, thus representing a highly advantageous advance in the art.

A most preferred use of the coating composition of the invention is as ahigh solids hot sprayable chip resistant primer for use on a bare metalsubstrate such as for an automotive vehicle body which is subject tochipping. Primer compositions typically are pigmented and any pigmentscommonly included in primer compositions for metal substrates andacrylic dispersion topcoats such as, for example, carbon black, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO₂,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition.

The pigment-to-binder ratio of the chip resistant primer may be fromabout 0.5:1 to about 2:1 by weight, respectively; it is preferred,however, to use a primer having a pigment-to-binder ratio of from about1:1 to about 1.5:1 by weight, respectively.

In preferred embodiments of this invention, pigments and thixotropicagents desireably are dispersed with epoxy ester resins. One type ofepoxy ester resin useful for this purpose comprises the reaction productof diepoxide, diphenol and/or dimer acid and a mixture of Soya fattyacid and propionic acid (See Example 4). Other epoxy ester resins usefulfor this purpose are those disclosed in U.S. application Ser. Nos.48,886 filed June 14, 1982 (abandoned), 431,465 filed Sept. 30, 1982(abandoned), and in U.S. Pat. No. 4,491,641, all assigned to theassignee of this application. These resins comprise the simultaneousreaction product of diepoxide with (i) diphenol, dicarboxylic acid or amixture of them in chain extension reaction and (ii) fatty acid in chainterminating esterification reaction Still other suitable epoxy resinsuseful for dispersing pigment and thixotropic agents will be apparent tothe skilled of the art in view of the present disclosure.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared simplyby incorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutionscombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a high solids, hot sprayable, automotive vehiclechip resistant primer, the solvent will comprise preferably about 20 toabout 40 percent by weight of the total coating compositions, althoughof course, larger or smaller amounts may be utilized depending upon thesolids content desired.

The primer is generally maintained at about 65 to about 80 percentsolids content for hot spraying purposes with conventional thinners suchas aromatic hydrocarbons, commercial petroleum cuts which areessentially aromatic, and the like, and sprayed onto the metal base orother substrate and cured. The primer may be applied in greaterthickness of 1 to 25 mils wet, preferably 10 to 25 mils wet, in order toobtain final coatings in the desired range of 5-11 mils dry in regionshighly susceptible to chipping and is then feathered down in thicknessto the thickness of paints in areas not receiving a chip resistantprimer. The primer is cured at elevated temperatures by any convenientmeans such as baking ovens or banks of infra-red heat lamps. Curingtemperatures are preferably from about 135°C. to about 165°C., althoughcuring temperatures from about 100°C. to about 230°C. may be employed,if desired.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that these specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE 1 Preparation of Hydroxy Functional Epoxy Ester Resin

In a suitable reactor were charged 519 parts of Epon 829 (trademark,Shell Chemical Company, diepoxide), 137 parts of bisphenol-A and 169parts of Empol 1016 (trademark, Emery, Ind., Inc., dimer acid). Themixture was brought up to 160°C. at which point an exothermic reactionraised the temperature to 185°C. The mixture was kept at 175°C. for onehour and then cooled to 120°C. At this point the acid number wasmeasured to be less than one. 92 parts of diethanol amine and 190 partsof Solvesso 100 were added and the temperature was raised to 150°C. Thebatch was kept at this temperature for one hour. 218 parts of N-methylpyrrolidone were added and the mixture was allowed to cool. Theresulting product had a viscosity of Z₅ at 64.4% solids.

EXAMPLE 2 Preparation of Hydroxy Functional Epoxy Ester Resin

In a suitable reactor were charged 582 parts of Eponex (trademark, ShellChemical Company, diepoxide), 137 parts of bisphenol A, 169 parts ofEmpol 1016 (trademark, Emery Ind., Inc., dimer acid) and 0.5 parts ofsodium carbonate. The mixture was brought up to 160°C. at which point anexothermic reaction raised the temperature to 195°C. The mixture waskept at 175°C. for one hour and then cooled to 120°C. At this point theacid number was measured to be less than one. 92 parts of diethanolamine and 150 parts of Solvesso 100 were added and the temperature wasraised to 150°C. The batch was kept at this temperature for one hour.377 parts of N-methyl pyrrolidone were added and the mixture was allowedto cool. The resulting product had a viscosity of Z₁ at 65.0% solids.

EXAMPLE 3 Preparation of Hydroxy Functional Epoxy Ester Resin

In a suitable reactor were charged 355 parts of Araldide RD-2(trademark, Ciba-Geigy Corporation, diepoxide), 137 parts ofbisphenol-A, 169 parts of Empol 1016 (trademark, Emery, Ind., Inc.,dimer acid) and 0.5 parts of sodium carbonate. The mixture was broughtup to 160°C. at which point an exothermic reaction raised thetemperature to 195°C. The mixture was kept at 175°C. for one hour andthen cooled to 120°C. At this point the acid number was measured to beless than one. 92 parts of diethanol amine and 150 parts of Solvesso 100were added and the temperature was raised to 150°C. The batch was keptat this temperature for one hour. 255 parts of N-methyl pyrrolidone wereadded and the mixture was allowed to cool. The resulting product had aviscosity of Z at 65.0% solids.

EXAMPLE 4 Preparation of Epoxy Ester Dispersing Resin

Into a suitable reactor were charged 1280 parts Epon 829 (trademark,Shell Chemical Company, diepoxide), 954 parts Empol 1016 (trademark,Emery Ind., Inc., dimer acid), 364 parts Soya fatty acid, 268 parts2,2-bis(hydroxymethyl) propionic acid, and 13 parts lithiumneodeconoate. The temperature of the mixture was brought up to about180°C., at which point an exothermic reaction takes place that raisedthe temperature to about 200°C. After one hour, the acid number wasfound to be less than 2. 940 parts Solvesso 100 and 305 parts Solvesso150 were added, and the mixture was cooled. The resin had a viscosity ofZ₇ at 70.0% solids.

EXAMPLE 5 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 870 parts methylethyl ketoxime and180 parts Solvesso 100. 1330 parts of PAPI 27 (trademark, The UpJohnChemical Co., aromatic polyisocyanate) was added dropwise to the mixtureover two hours; the reaction temperature rose from room temperature to80° -95°C. 39 parts 2-ethylhexanol was added to the mixture and thetemperature of the mixture was maintained at 85° -95°C. for one hour. Atthat point, 816 parts of M-pyrol was added and the mixture was cooled.The resulting resin was dark brown and had a viscosity of 6000 cps at67.0% solids.

EXAMPLE 6 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 537 parts methylethyl ketoxime. 784parts PAPI 94 (trademark, The UpJohn Chemical Co., aromaticpolyisocyanate) was added dropwise over two hours; the reactiontemperature rose from room temperature to 85° -95°C. The mixture wasmaintained at 85° -95°C. for one hour. The mixture was then checked toinsure complete reaction of the isocyante by infrared spectroscopy. Atthat point, 300 parts methylamyl ketone and 150 parts M-pyrol was addedand the mixture was cooled. The resulting resin was dark brown and was75% solids.

EXAMPLES 7-10 Preparation of Blocked Polyisocyanate Crosslinking Agent

Blocked polyisocyanate crosslinkers according to the invention wereprepared in the manner of Example 6. The components employed are shownin the table below.

    ______________________________________                                                      Example                                                                       7    8        9      10                                         Composition     Parts                                                         ______________________________________                                        L--2991 A*      360    360      360                                           Desmodur IL*                         525                                      ethyl amyl ketoxime                                                                           174                   87                                      benzotriazole          238                                                    epsilon-caprolactone            228                                           N--methyl pyrolidone                                                                          133    150      195  461                                      % solids         80    80.1     75.1  57                                      Viscosity       Z.sub.1                                                                              Z.sub.6  Z.sub.2                                                                            Z                                        ______________________________________                                         *Trademarks of Mobay Chemical Co.; L--2991 A is a biurette of                 hexamethylene diisocyanate; Desmodur IL is a polyisocyanurate of tolylene     diisocyanate.                                                            

EXAMPLE 11 Millbase Preparation

In a one gallon can or ballmill were charged the following materials andone quart of diagonal shot. The mixture was placed on a roller mill for16-24 hours to reach a 7+hegman dispersion. At that point, the letdownwas added, and the mixture was run an additional hour on the rollermill.

    ______________________________________                                                           Parts                                                      ______________________________________                                        Hi-Sol #3*           585                                                      2-Ethyl Hexanol       95                                                      Polyethylene Wax      70                                                      Anti-Terra-U**        40                                                      Resin of Example 4   103                                                      Barytes              2259                                                     TiO.sub.2            429                                                      Carbon Black          29                                                      Strontium Chromate   143                                                      Letdown: Resin of Example 4                                                                        247                                                      ______________________________________                                         *Trademark of Ashland Chemical Co., Columbus, Ohio; HiSol #3 is an            aromatic solvent.                                                             **Trademark of Byk Mallinckrodt, Wallingford, CT 06492; AntiTerra-U is an     antisettling and wetting agent.                                          

EXAMPLE 12 Bentone Gel Preparation

To a clean Ball Mill were charged the following:

    ______________________________________                                                              Parts                                                   ______________________________________                                        Solvesso 150            513                                                   Propylene Carbonate      13                                                   Bentone 38               30                                                   Grind 30 minutes, then add:                                                   Resin of Example 4      384                                                   Grind approximately 2 Hrs. to 8 Hegman                                        Letdown with:                                                                 Solvesso 150             60                                                                           1000                                                  ______________________________________                                    

EXAMPLES 13-15

Coating compositions according to the invention were formulated as shownbelow.

    ______________________________________                                                        Example                                                                       13      14     15                                             Composition       Parts                                                       ______________________________________                                        Resin of Example 1                                                                              1384                                                        Resin of Example 2          1384                                              Resin of Example 3                 1384                                       Millbase of Example 11                                                                          5788      5788   5788                                       TONE 0260.sup.1   950        950   950                                        Bentone Gel of Example 12                                                                       2315      2315   2315                                       Crosslinker of Example 5                                                                        984              984                                        Crosslinker of Example 6    1050                                              Dislon.sup.2      114        120   114                                        Cab-O-Sil.sup.3   142              142                                        ______________________________________                                         .sup.1 Trademark of Union Carbide, Danbury Connecticut, TONE 0260 is a        polycaprolactone diol.                                                        .sup.2 Trademark of Kusumoto Chemicals, Ltd.; Dislon is an antisagging        agent.                                                                        .sup.3 Trademark of Cabot Corp., Boston, Mass.; CabO-Sil is a foamed          silica (antisettling agent).                                             

The coating compositions were prepared by sequential mixing in a 5gallon working capacity EMCO Proto-Lab SW Mill (trademark), Epworth Mfg.Co., South Haven, MI, set at 900 rpm. Resin and Dislon (trademark) werefirst mixed for approximately 10 minutes and then millbase, Bentone geland crosslinker were added sequentially while mixing. Finally Cab-0-Sil(trademark) was added and the composition mixed until a grind of 6+onthe Hegman scale was obtained.

The above compositions were sprayed at 140° -160°C. using hot-sprayequipment commercially available from Nordson Corp. Unpolished Bonderitesteel panels were sprayed and baked at 135°C. for 20 minutes. Thethickness of the coating tested varied from 5 mils to 12 mils. Thepanels were top-coated with white enamel and tested for chip resistanceusing 10 pts. of gravel in the gravelometer test. All the abovecompositions exhibited excellent chip resistance. In addition, panelswere tested for corrosion resistance (500 hrs. salt spray test, scribedpanels) and humidity resistance with excellent results.

EXAMPLES 16-19

Additional coating compositions according to the invention are shownbelow.

    ______________________________________                                                        Example                                                                       16   17       18     19                                       Composition       Parts                                                       ______________________________________                                        Resin of Example 1                                                                              1385   1385     1385 1385                                   TONE 0260.sup.1    950    950      950  950                                   Millbase of Example 11                                                                          5788   5788     5788 5788                                   Gel of Example 12 2315   2315     2315 2315                                   Crosslinker of Example 7                                                                         922                                                        Crosslinker of Example 8  922                                                 Crosslinker of Example 9           984                                        Crosslinker of Example 10              1294                                   Dislon.sup.2       100    100      100  100                                   ______________________________________                                         .sup.1 Trademark of Union Carbide, Danbury Connecticut, TONE 0260 is a        polycaprolactone diol.                                                        .sup.2 Trademark of Kusumoto Chemicals, Ltd.; Dislon is an antisagging        agent.                                                                   

INDUSTRIAL APPLICATION

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as a hotsprayable, high solids coating composition suitable for use as a chipresistant automotive vehicle primer adapated for use on body panel areassubject to chipping by stones, gravel and other road debris.

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchapparent modifications fall within the true scope of this invention andbe included within the terms of the appended claims.

What is claimed is:
 1. An organic solvent based, thermosetting coatingcomposition comprising:(A) hydroxy functional epoxy ester resin whichhas a number average molecular weight (Mn) between about 1,000 and about4,000 and which is the reaction product of hydroxy functional secondaryamine, in chain terminating reaction, in approximately 1 to 1 equivalentratio with the chain extension reaction product of diepoxide reactedsubstantially simultaneously with diphenol and dicarboxylic acid inamounts sufficient to give a weight per epoxide between about 500 andabout 2,500; (B) linear polycaprolactone diol having a molecular weightof between about 1500 and about 5000, wherein said (A) and (B) areincluded in said composition in a weight ratio between about 4:1 and1:4; and (C) blocked polyisocyanate crosslinking agent comprising atleast two isocyanate groups which have been blocked by reaction with anactive hydrogen bearing blocking agent, which crosslinking agentde-blocks at the cure temperature of said composition, said crosslinkingagent being included in said composition in an amount equal to betweenabout 10 and about 50 percent of the combined weight of said (A) and (B)in said composition.
 2. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said diepoxide isreacted substantially simultaneously with said diphenol and dicarboxylicacid in amounts sufficient to give a weight per epoxide of between about500 and about 1,500.
 3. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said polycaprolactonediol has a molecular weight between about 2000 and
 4000. 4. A solventbased, thermosetting coating composition in accordance with claim 1,wherein said (A) and (B) are included in said composition in a weightratio of about 1:1.
 5. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said blockedpolyisocyanate crosslinking agent is included in said composition in anamount equal to between about 20 and about 40 percent of the combinedweight of components (A) and (B) in said composition.
 6. A solventbased, thermosetting coating composition in accordance with claim 1,wherein said diepoxide is selected from the group consisting ofbisphenol-A epichlorohydrin epoxy resin, hydantoin epoxy resin, cyclicand acyclic aliphatic diepoxides, and mixtures thereof.
 7. A solventbased, thermosetting coating composition in accordance with claim 1,wherein said diphenols are selected from the group consisting ofbisphenol-A, bisphenol-B, bisphenol-F and mixtures thereof.
 8. A solventbased, thermosetting coating composition in accordance with claim 1,wherein said dicarboxylic acid is selected from the group consisting ofsaturated or unsaturated, cyclic or acyclic, aliphatic or aromaticdicarboxylic acids and mixtures thereof.
 9. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid dicarboxylic acid is selected from the group consisting ofsubstantially saturated, acyclic, aliphatic dimer acids of about 4-42carbons and mixtures thereof.
 10. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said hydroxy functionalsecondary amine is selected from the group having the general formula:##STR10## wherein R and R' are selected from aliphatic, cycloaliphaticand aromatic radicals which will not interfere with the chaintermination reaction of the diepoxide and the hydroxy functionalsecondary amine to form the hydroxy functional epoxy ester resin, andwherein X is selected from the group consisting of hydrogen and hydroxylradical.
 11. A solvent based, thermosetting coating composition inaccordance with claim 10, wherein said hydroxy functional secondaryamine bears primary hydroxyl functionality.
 12. A solvent based,thermosetting coating composition in accordance with claim 11, whereinsaid hydroxy functional secondary amine is selected from the groupconsisting of diethanol amine, methylethanol amine, dipropanol amine andmethylpropanol amine.
 13. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said linearpolycaprolactone diol is the product of polymerization of lactonemonomers in the presence of initiator compounds having two functionalgroups each having an active hydrogen capable of opening the lactonering at a temperature of between about 50°C. and about 300°C., saidlactone monomers having the general formula: ##STR11## wherein n is atleast 4, at least n+2 R's are H and the remaining R's are substituentsselected from the group consisting of alkyl, cycloalkyl, alkoxy andsingle ring aromatic hydrocarbon radicals.
 14. A solvent based,thermosetting coating composition in accordance with claim 13, whereinsaid initiator compounds are selected from the group consisting ofdiamines, diols, aminoalcohols, diacids and hydroxy carboxylic acids.15. A solvent based, thermosetting coating composition in accordancewith claim 13, wherein said lactone monomers comprise unsubstitutedepsilon-caprolactone monomers.
 16. A solvent based, thermosettingcoating composition in accordance with claim 1, wherein:(a) saidpolycaprolactone diol is formed by polymerizing lactone monomers in thepresence of intiator compounds having two functional groups each havingan active hydrogen capable of opening the lactone ring at a temperatureof between about 50°C. and 300°C., said lactone monomers having thegeneral formula: ##STR12## wherein n is at least 4, at least n+2 R's arehydrogen, and the remaining R's are substituents selected from the groupconsisting of alkyl, cycloalkyl, alkoxy and single ring aromatichydrocarbon radicals; (b) the chain extended diepoxide is the reactionproduct of said diepoxide selected from the group consisting ofbisphenol-A epichlorohydrin epoxy resin, hydantoin epoxy resin, cyclicand acyclic aliphatic diepoxide, and mixtures thereof, with (i) saiddiphenol selected from the group consisting of those having the generalformula: ##STR13## and mixtures thereof, wherein R is a divalent,organic, linking moiety substantially unreactive with the epoxyfunctionality of said diepoxide and (ii) said dicarboxylic acid isselected from the group consisting of substantially saturated, acyclic,aliphatic dimer acids of about 4-42 carbons and mixtures thereof; (c)said hydroxy functional secondary amine is selected from the grouphaving the general formula: ##STR14## wherein R and R' are selected fromthe group consisting of aliphatic, cycloaliphatic and aromatic radicalswhich will not interfere with the chain termination reaction of epoxideand the hydroxy functional secondary amine, X is selected from the groupconsisting of hydrogen and hydroxyl radical, and at least a portion ofhydroxyl groups on said hydroxy functional secondary amine are primary.17. A solvent based, thermosetting coating composition in accordancewith claim 1, wherein said blocked polyisocyanate crosslinking agentcomprises blocked polymethylene polyphenol isocyanate which unblockedhas the formula: ##STR15## wherein n equals 1 to
 3. 18. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid blocked polyisocyanate crosslinking agent is the reaction productof:(a) the reaction product of (i) organic diisocyanate represented bythe formula:

    OCN--R--NCO

    wherein R is selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals and combinations thereof and wherein one of the isocyanate groups thereof is a more reactive isocyanate group than the other isocyanate group and (ii) sufficient active hydrogen containing blocking agent to react with substantially all of said more reactive isocyanate groups; and

(b) sufficient polyol to react with substantially all of said otherisocyanate groups.
 19. A solvent based, thermosetting coatingcomposition in accordance with claim 1, adapted to be used as a chipresistant primer to be sprayed at elevated temperature, wherein thesolids level of the composition is in the range of 60-80% by weight. 20.An organic solvent based, thermosetting coating compositioncomprising:(A) hydroxy functional epoxy ester resin which has a numberaverage molecular weight (Mn) between about 1,000 and about 4,000 andwhich is the reaction product of hydroxy functional secondary amine, inchain terminating reaction, in approximately 1 to 1 equivalent ratiowith the chain reaction product of diepoxide reacted substantiallysimultaneously with diphenol and dicarboxylic acid in amounts sufficientto give a weight per epoxide between about 500 and about 2,500, saiddiepoxide being selected from the group consisting of bisphenol-Aepichlorohydrin epoxy resin, hydantoin epoxy resin, cyclic and acyclicaliphatic diepoxide, and mixtures thereof, said diphenol being selectedfrom the group consisting of bisphenol-A, bisphenol-B, bisphenol-F andmixtures thereof, and said dicarboxylic acid being selected from thegroup consisting of essentially of the dimerization product of C-18fatty acid, (B) linear polycaprolactone diol having a molecular weightof between about 1500 and 5000 and being the product of polymerizationof epsilon-caprolactone monomers in the presence of compounds having twofunctional group each having an active hydrogen capable of opening thelactone ring at a temperature of between about 50°C. and about 300°C.,wherein said (A) and (B) are included in said composition in a weightratio between about 4:1 and 1:4; (C) blocked polyisocyanate crosslinkingagent comprising at least two isocyanate groups which have been blockedby reaction with an active hydrogen bearing blocking agent, whichcrosslinking agent de-blocks at the cure temperature of saidcomposition, said blocked polyisocyanate being selected from blockedaliphatic, aromatic, cycloalkylene, aliphatic aromatic, and nuclearsubstituted aromatic polyisocyanates and being included in saidcomposition in an amount equal to between about 10 and about 50 percentof the combined weight of said (A) and (B) in said composition.